JP2005094370A

JP2005094370A - Image scanner

Info

Publication number: JP2005094370A
Application number: JP2003325092A
Authority: JP
Inventors: Makio Kondo; 牧雄近藤
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2003-09-17
Filing date: 2003-09-17
Publication date: 2005-04-07

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image scanner which can set the optimum value for taking noise in black correction level calculation, and prevent the occurrence of bad influence due to frequently repeated changes in the black correction level. <P>SOLUTION: In the image scanner provided with a line sensor, a black correction level calculating section and a black correcting section, the black correction level calculating section is provided with a light-shielding level calculator (201) for obtaining a light-shielding level at the number of reading bits or the number of bits more than that from light-shielding levels of a plurality of light-shielding pixels in one line read by the line sensor; a different value calculating section (202) for obtaining a different value between the light-shielding level and the black level of a previous line; a black level calculating means (204) for comparing the difference value with a predetermined value, updating the black level of the previous line by the number of read bits or the number of bits more than that from a comparison result to obtain the black level of a main line; and a black correction level calculating means (203) for obtaining the black correction level of the main line of the number of read bits from the black level of the main line and outputting the obtained correction level to the black correction section. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本発明はデジタルコピー、ファクシミリ、スキャナ等に用いられる画像読取り装置に関し、特に、原稿面を光学的に走査し、１次元ラインセンサによって画像読取りを行う画像読取り装置であって、ラインセンサの有効画素領域外に設けられた遮光画素の読取りレベルから黒補正レベルを求め、各有効画素の読取りレベルから黒補正レベルを減算することで真の読取りレベルを得る画像読取り装置に関する。 BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus used for a digital copy, a facsimile, a scanner, and the like, and more particularly to an image reading apparatus that optically scans a document surface and reads an image by a one-dimensional line sensor. The present invention relates to an image reading apparatus that obtains a true reading level by obtaining a black correction level from a reading level of a light-shielding pixel provided outside a region and subtracting the black correction level from the reading level of each effective pixel.

入力光を光電変換し、入力光量に比例した電気信号を出力する光電変換素子ＣＣＤ（Charge Coupled Device）に代表されるイメージセンサでは、イメージセンサの特性として、光入力がない状態でも暗出力レベルの出力があり、光入力された状態では入力光量レベルに暗出力レベルが付加された出力となる。そのため、一般的にデジタルコピー、ファクシミリ、スキャナ等に用いられる画像読取り装置では、真の画像レベルを得るために、イメージセンサの出力レベルからイメージセンサへの光入力がない暗出力レベルを差し引く補正処理(黒補正)が行われる。 In an image sensor represented by a photoelectric conversion device CCD (Charge Coupled Device) that photoelectrically converts input light and outputs an electrical signal proportional to the input light amount, the image sensor has a dark output level even in the absence of light input. When there is an output and light is input, an output is obtained by adding a dark output level to the input light amount level. Therefore, in an image reading apparatus generally used for digital copy, facsimile, scanner, etc., in order to obtain a true image level, a correction process for subtracting a dark output level without light input to the image sensor from an output level of the image sensor. (Black correction) is performed.

黒補正の方法としては、光源消灯時に各有効画素の出力レベルを保存し、読取り時に各有効画素の出力レベルから、消灯時の出力レベルを減算する方法もあるが、画像読取り装置のイメージセンサとして代表的な１次元ラインセンサであるＣＣＤでは、センサの有効画素領域外に光入力を遮光した画素領域が設けられており、この遮光画素の読取りレベルから黒補正を行うレベル(黒補正レベル)を求め、各有効画素の読取りレベルから黒補正レベルを減算する方法が一般的に行われている（例えば、特許文献１参照。）。 As a black correction method, there is a method of storing the output level of each effective pixel when the light source is turned off and subtracting the output level at the time of turning off from the output level of each effective pixel at the time of reading. In a CCD, which is a typical one-dimensional line sensor, a pixel area where light input is shielded is provided outside the effective pixel area of the sensor, and the black correction level (black correction level) is determined from the read level of the shielded pixel. A method of obtaining and subtracting the black correction level from the reading level of each effective pixel is generally performed (see, for example, Patent Document 1).

後者の具体的な黒補正方法としては、ラインセンサの遮光画素領域にある複数画素の読取りレベルを平均して黒レベルとする方法が良く知られている。なお、この方法で黒レベルは、複数画素の平均化により、読取りbit数よりもbit数を増やすことができるが、黒補正処理後のbit数を増やさないよう、黒レベルを読取りbit数に丸めて黒補正レベルとし、有効画素の読取りレベルからは黒補正レベルを減算するのが一般的である。
また、更に黒レベルのノイズを抑えるため、複数の遮光画素の読取りレベルを平均した遮光レベルを副走査ライン方向に重加算平均して黒レベルとする方法などもある。 As the latter specific black correction method, a method of averaging the read levels of a plurality of pixels in the light-shielded pixel region of the line sensor to obtain a black level is well known. In this method, the black level can be increased more than the number of read bits by averaging multiple pixels, but the black level is rounded to the number of read bits so as not to increase the number of bits after black correction processing. In general, the black correction level is used, and the black correction level is subtracted from the effective pixel reading level.
Further, in order to further suppress black level noise, there is a method in which the light shielding level obtained by averaging the reading levels of a plurality of light shielding pixels is averaged in the sub-scanning line direction to obtain the black level.

特開平１０-１１７２７８号公報Japanese Patent Laid-Open No. 10-117278

しかしながら、これら従来の方法では、複数の遮光画素の読取りレベルを平均して黒レベルとする方法では、近年の読取りbit数の高階調化もあり、1ライン内の遮光画素の平均だけでは充分にノイズを取りきれない場合がある。 However, in these conventional methods, the method of averaging the read level of a plurality of light-shielded pixels to a black level also has a recent increase in the number of read bits, and the average of the light-shielded pixels in one line is sufficient. Noise may not be removed.

また、副走査ラインに重加算を併用する方法では、遮光レベルと黒レベルのbit数が同じ場合には一般的に、次の式で重加算の演算が行われる。なお、本ライン黒レベルとは対象となる読取りラインにおける黒レベルであり、前ライン黒レベルとは本ラインの１つ前の読取りラインにおける黒レベルのことである。 Further, in the method of using multiple addition in combination with the sub-scanning line, when the number of bits of the light shielding level and the black level is the same, generally, the calculation of the multiple addition is performed by the following equation. The main line black level is the black level in the target read line, and the previous line black level is the black level in the read line immediately before the main line.

(本ライン黒レベル)＝{(遮光レベル)＋(前ライン黒レベル)×(a−1)}／a
（ただし、a＝2,3,4,…） (Main line black level) = {(Light shielding level) + (Previous line black level) x (a-1)} / a
(However, a = 2,3,4, ...)

この重加算では、例えば切捨て処理の場合、遮光レベルが(前ライン黒レベル)から（(前ライン黒レベル)＋a−1）までは、(本ライン黒レベル)の値は(前ライン黒レベル)の値から変化しない。したがって、定数aはノイズを取るのに適切な値とすることが望まれるが、一方で、ハードウェアで演算を行う場合に、定数aは２の乗数にする方がハード化は容易である。定数aを自由に可変できるようにするとハードウェアが過剰に規模が大きなってしまい現実的でないため、自然と用意できるハードウェアの制約から定数aの設定自由度は乏しいものとなる。 In this multi-addition, for example, in the case of truncation processing, the value of (main line black level) is (front line black level) when the shading level is from (front line black level) to ((front line black level) + a-1). No change from the value of. Therefore, it is desired that the constant a be an appropriate value for taking noise, but on the other hand, when the calculation is performed by hardware, it is easier to make the constant a a multiplier of 2. If the constant a can be freely changed, the hardware becomes excessively large and unrealistic. Therefore, the degree of freedom in setting the constant a is poor due to the restriction of hardware that can be prepared naturally.

更に、黒補正レベルは読取りbit数よりもbit数を増やし精度を増すこともできるが、読取りbit数自体は変わらないので、性能アップが僅かであるのに対して黒補正処理後のbit数の増加に伴うコストアップが大きくなる。そのため、黒レベルを精度良く求めても、黒補正レベルは読取bit数に丸めるのが一般的である。この丸めにおいて、黒レベルが丸めのスレッシュにあると、黒レベルの僅かな変化で黒補正レベルの値が変わるため、黒補正レベルが頻繁に変化を繰り返して画像に悪影響を生じることがある。 In addition, the black correction level can be increased by increasing the number of bits over the number of read bits, but the number of read bits does not change, so the performance is slightly improved, but the number of bits after black correction processing is small. The cost increases with the increase. Therefore, even if the black level is obtained with high accuracy, the black correction level is generally rounded to the number of read bits. In this rounding, if the black level is at the rounding threshold, the black correction level changes with a slight change in the black level, so that the black correction level frequently changes, which may adversely affect the image.

本発明は、以上の従来技術における問題に鑑みてなされたものであり、黒補正レベル算出においてノイズを取るのに最適な値の設定ができ、黒補正レベルが頻繁に変化を繰り返して画像に悪影響を生じることのない画像読取り装置を提供することを目的とする。 The present invention has been made in view of the above-described problems in the prior art, and it is possible to set an optimum value for taking noise in black correction level calculation, and the black correction level frequently changes and adversely affects an image. It is an object of the present invention to provide an image reading apparatus that does not cause the above-described problem.

前記課題を解決するために提供する請求項１の発明に係る画像読取り装置は、原稿面を光学的に走査して１次元ライン状に読取ることを繰り返して行い、そのラインごとに画像データを出力するラインセンサと、該ラインセンサの有効画素領域外に設けられた遮光画素の読取りレベルから黒補正レベルを求める黒補正レベル算出部と、読取りラインごとに前記画像データの有効画素の読取りレベルから前記黒補正レベルを減算することで真の読取りレベルを得る黒補正部とを備えた画像読取り装置において、前記黒補正レベル算出部は、前記ラインセンサの特定位置の遮光画素の読取りレベルである遮光レベルと前ラインの黒レベルとの差分値を求める差分値算出手段と、該差分値と所定値とを比較し、その比較結果から読取りbit数あるいはそれ以上のbit数で前ラインの黒レベルを更新して本ラインの黒レベルを求める黒レベル算出手段と、その本ラインの黒レベルから読取りbit数の本ラインの黒補正レベルを求めて前記黒補正部に出力する黒補正レベル算出手段と、を備えることを特徴とする。 The image reading apparatus according to the first aspect of the present invention is provided to solve the above-mentioned problems. The image reading apparatus optically scans a document surface and repeatedly reads the original surface into a one-dimensional line, and outputs image data for each line. A line correction sensor, a black correction level calculation unit for obtaining a black correction level from a read level of a light-shielded pixel provided outside the effective pixel area of the line sensor, and a read level of the effective pixel of the image data for each read line. In the image reading apparatus including a black correction unit that obtains a true reading level by subtracting a black correction level, the black correction level calculation unit is a light shielding level that is a reading level of a light shielding pixel at a specific position of the line sensor. And a difference value calculating means for obtaining a difference value between the black level of the previous line and the difference value and a predetermined value, and from the comparison result, the number of read bits or A black level calculation means for obtaining the black level of the main line by updating the black level of the previous line with the number of bits greater than this, and obtaining the black correction level of the main line of the number of read bits from the black level of the main line, And a black correction level calculation means for outputting to the correction unit.

前記課題を解決するために提供する請求項２の発明に係る画像読取り装置は、原稿面を光学的に走査して１次元ライン状に読取ることを繰り返して行い、そのラインごとに画像データを出力するラインセンサと、該ラインセンサの有効画素領域外に設けられた遮光画素の読取りレベルから黒補正レベルを求める黒補正レベル算出部と、読取りラインごとに前記画像データの有効画素の読取りレベルから前記黒補正レベルを減算することで真の読取りレベルを得る黒補正部とを備えた画像読取り装置において、前記黒補正レベル算出部は、前記ラインセンサの特定位置の遮光画素の読取りレベルである遮光レベルと前ラインの黒レベルとの差分値を求める差分値算出手段と、該差分値を前ラインまでの差分値の累積値に加算し、新たな累積値を求める累積値算出手段と、その求められた累積値と所定値とを比較し、その比較結果から読取りbit数あるいはそれ以上のbit数で前ラインの黒レベルを更新して本ラインの黒レベルを求める黒レベル算出手段と、その本ラインの黒レベルから読取りbit数の本ラインの黒補正レベルを求めて前記黒補正部に出力する黒補正レベル算出手段と、を備えることを特徴とする。 An image reading apparatus according to the invention of claim 2 provided to solve the above-described problems is to repeatedly scan a document surface optically and read it in a one-dimensional line, and output image data for each line. A line correction sensor, a black correction level calculation unit for obtaining a black correction level from a read level of a light-shielded pixel provided outside the effective pixel area of the line sensor, and a read level of the effective pixel of the image data for each read line. In the image reading apparatus including a black correction unit that obtains a true reading level by subtracting a black correction level, the black correction level calculation unit is a light shielding level that is a reading level of a light shielding pixel at a specific position of the line sensor. Difference value calculating means for calculating a difference value between the black level of the previous line and the previous line, and adding the difference value to the accumulated value of the difference value up to the previous line, The accumulated value calculation means to compare the obtained accumulated value with a predetermined value, and update the black level of the previous line with the number of read bits or more from the comparison result, and the black level of this line And a black correction level calculation means for obtaining the black correction level of the main line having the number of read bits from the black level of the main line and outputting the black correction level to the black correction unit.

前記課題を解決するために提供する請求項３の発明に係る画像読取り装置は、原稿面を光学的に走査して１次元ライン状に読取ることを繰り返して行い、そのラインごとに画像データを出力するラインセンサと、該ラインセンサの有効画素領域外に設けられた遮光画素の読取りレベルから黒補正レベルを求める黒補正レベル算出部と、読取りラインごとに前記画像データの有効画素の読取りレベルから前記黒補正レベルを減算することで真の読取りレベルを得る黒補正部とを備えた画像読取り装置において、前記黒補正レベル算出部は、前記ラインセンサの特定位置の遮光画素の読取りレベルである遮光レベルと前ラインの黒レベルとの差分値を求める差分値算出手段と、該差分値と所定値２とを比較し、その比較結果から前ラインまでの累積値を更新して、新たな累積値を求める手段と、その求められた累積値と所定値１とを比較し、その比較結果から読取りbit数あるいはそれ以上のbit数で前ラインの黒レベルを更新して本ラインの黒レベルを求める黒レベル算出手段と、その本ラインの黒レベルから読取りbit数の本ラインの黒補正レベルを求めて前記黒補正部に出力する黒補正レベル算出手段と、を備えることを特徴とする。 According to a third aspect of the present invention, there is provided an image reading apparatus according to a third aspect of the present invention, wherein the original surface is optically scanned and read repeatedly in a one-dimensional line, and image data is output for each line. A line correction sensor, a black correction level calculation unit for obtaining a black correction level from a read level of a light-shielded pixel provided outside the effective pixel area of the line sensor, and a read level of the effective pixel of the image data for each read line. In the image reading apparatus including a black correction unit that obtains a true reading level by subtracting a black correction level, the black correction level calculation unit is a light shielding level that is a reading level of a light shielding pixel at a specific position of the line sensor. And a difference value calculating means for obtaining a difference value between the black level of the preceding line and the predetermined value 2 and comparing the difference value with the predetermined value 2 The value is updated and a means for obtaining a new accumulated value is compared with the obtained accumulated value and the predetermined value 1. From the comparison result, the black level of the previous line is determined by the number of read bits or more. A black level calculating means for obtaining a black level of the main line by updating, a black correction level calculating means for obtaining a black correction level of the main line of the number of read bits from the black level of the main line and outputting the black correction level to the black correction unit; It is characterized by providing.

前記課題を解決するために提供する請求項４の発明に係る画像読取り装置は、原稿面を光学的に走査して１次元ライン状に読取ることを繰り返して行い、そのラインごとに画像データを出力するラインセンサと、該ラインセンサの有効画素領域外に設けられた遮光画素の読取りレベルから黒補正レベルを求める黒補正レベル算出部と、読取りラインごとに前記画像データの有効画素の読取りレベルから前記黒補正レベルを減算することで真の読取りレベルを得る黒補正部とを備えた画像読取り装置において、前記黒補正レベル算出部は、前記ラインセンサが読取った１ラインの複数の遮光画素の読取りレベルから読取りbit数、あるいはそれ以上のbit数で遮光レベルを求める遮光レベル算出手段と、該遮光レベルと前ラインの黒レベルとの差分値を求める差分値算出手段と、該差分値と所定値とを比較し、その比較結果から読取りbit数あるいはそれ以上のbit数で前ラインの黒レベルを更新して本ラインの黒レベルを求める黒レベル算出手段と、その本ラインの黒レベルから読取りbit数の本ラインの黒補正レベルを求めて前記黒補正部に出力する黒補正レベル算出手段と、を備えることを特徴とする。 The image reading apparatus according to the invention of claim 4 provided to solve the above-mentioned problem is to repeatedly scan the original surface optically and read it in a one-dimensional line, and output image data for each line. A line correction sensor, a black correction level calculation unit for obtaining a black correction level from a read level of a light-shielded pixel provided outside the effective pixel area of the line sensor, and a read level of the effective pixel of the image data for each read line. And a black correction unit that obtains a true reading level by subtracting the black correction level, wherein the black correction level calculation unit reads the reading levels of a plurality of light-shielding pixels in one line read by the line sensor. The light-shielding level calculation means for obtaining the light-shielding level with the number of bits read from or above, and the difference between the light-shielding level and the black level of the previous line A difference value calculating means for determining the black level of the main line by comparing the difference value with a predetermined value and updating the black level of the previous line with the number of read bits or more from the comparison result Level calculating means; and black correction level calculating means for obtaining a black correction level of the main line of the number of read bits from the black level of the main line and outputting the black correction level to the black correction unit.

前記課題を解決するために提供する請求項５の発明に係る画像読取り装置は、原稿面を光学的に走査して１次元ライン状に読取ることを繰り返して行い、そのラインごとに画像データを出力するラインセンサと、該ラインセンサの有効画素領域外に設けられた遮光画素の読取りレベルから黒補正レベルを求める黒補正レベル算出部と、読取りラインごとに前記画像データの有効画素の読取りレベルから前記黒補正レベルを減算することで真の読取りレベルを得る黒補正部とを備えた画像読取り装置において、前記黒補正レベル算出部は、前記ラインセンサの複数の遮光画素の読取りレベルから読取りbit数、あるいはそれ以上のbit数で遮光レベルを求める遮光レベル算出手段と、該遮光レベルと前ラインの黒レベルとの差分値を求める差分値算出手段と、該差分値を前ラインまでの差分値の累積値に加算し、新たな累積値を求める累積値算出手段と、その求められた累積値と所定値とを比較し、その比較結果から読取りbit数あるいはそれ以上のbit数で前ラインの黒レベルを更新して本ラインの黒レベルを求める黒レベル算出手段と、その本ラインの黒レベルから読取りbit数の本ラインの黒補正レベルを求めて前記黒補正部に出力する黒補正レベル算出手段と、を備えることを特徴とする。 The image reading apparatus according to the invention of claim 5 provided to solve the above-mentioned problem is to repeatedly scan the original surface optically and read it into a one-dimensional line, and output image data for each line. A line correction sensor, a black correction level calculation unit for obtaining a black correction level from a read level of a light-shielded pixel provided outside the effective pixel area of the line sensor, and a read level of the effective pixel of the image data for each read line. In the image reading apparatus provided with a black correction unit that obtains a true reading level by subtracting the black correction level, the black correction level calculation unit, the number of read bits from the reading level of the plurality of light-shielding pixels of the line sensor, Alternatively, a shading level calculation means for obtaining a shading level with more bits and a difference value calculation for obtaining a difference value between the shading level and the black level of the previous line. Means, adding the difference value to the accumulated value of the difference value up to the previous line, comparing the accumulated value calculating means for obtaining a new accumulated value, the obtained accumulated value and a predetermined value, and from the comparison result A black level calculation means for obtaining the black level of the main line by updating the black level of the previous line with the number of read bits or more, and the black correction level of the main line with the number of read bits from the black level of the main line. And a black correction level calculation means for obtaining and outputting to the black correction unit.

前記課題を解決するために提供する請求項６の発明に係る画像読取り装置は、原稿面を光学的に走査して１次元ライン状に読取ることを繰り返して行い、そのラインごとに画像データを出力するラインセンサと、該ラインセンサの有効画素領域外に設けられた遮光画素の読取りレベルから黒補正レベルを求める黒補正レベル算出部と、読取りラインごとに前記画像データの有効画素の読取りレベルから前記黒補正レベルを減算することで真の読取りレベルを得る黒補正部とを備えた画像読取り装置において、前記黒補正レベル算出部は、前記ラインセンサの複数の遮光画素の読取りレベルから読取りbit数、あるいはそれ以上のbit数で遮光レベルを求める遮光レベル算出手段と、該遮光レベルと前ラインの黒レベルとの差分値を求める差分値算出手段と、該差分値と所定値２とを比較し、その比較結果から前ラインまでの累積値を更新して、新たな累積値を求める手段と、その求められた累積値と所定値１とを比較し、その比較結果から読取りbit数あるいはそれ以上のbit数で前ラインの黒レベルを更新して本ラインの黒レベルを求める黒レベル算出手段と、その本ラインの黒レベルから読取りbit数の本ラインの黒補正レベルを求めて前記黒補正部に出力する黒補正レベル算出手段と、を備えることを特徴とする。 The image reading apparatus according to the invention of claim 6 provided to solve the above-mentioned problem is to repeatedly scan the original surface optically and read it in a one-dimensional line, and output image data for each line. A line correction sensor, a black correction level calculation unit for obtaining a black correction level from a read level of a light-shielded pixel provided outside the effective pixel area of the line sensor, and a read level of the effective pixel of the image data for each read line. In the image reading apparatus provided with a black correction unit that obtains a true reading level by subtracting the black correction level, the black correction level calculation unit, the number of read bits from the reading level of the plurality of light-shielding pixels of the line sensor, Alternatively, a shading level calculation means for obtaining a shading level with more bits and a difference value calculation for obtaining a difference value between the shading level and the black level of the previous line. Means for comparing the difference value with the predetermined value 2 and updating the accumulated value from the comparison result up to the previous line to obtain a new accumulated value; the obtained accumulated value and the predetermined value 1; And a black level calculation means for obtaining the black level of the main line by updating the black level of the previous line with the number of read bits or more from the comparison result, and the number of read bits from the black level of the main line Black correction level calculation means for obtaining a black correction level of the main line and outputting the black correction level to the black correction unit.

前記課題を解決するために提供する請求項７の発明に係る画像読取り装置は、請求項１〜６の発明において、前記黒レベル算出手段が、前記遮光レベルを本ラインの黒レベルとする機能を有し、該機能がレジスタ設定または読取り動作制御のハード信号で選択されることを特徴とする。 The image reading apparatus according to the invention of claim 7 provided to solve the above-mentioned problem is the invention according to claims 1 to 6, wherein the black level calculation means has a function of setting the light shielding level to the black level of this line. And the function is selected by a hard signal for register setting or reading operation control.

前記課題を解決するために提供する請求項８の発明に係る画像読取り装置は、請求項１，２，４，５の発明において、前記所定値は、レジスタ設定されることを特徴とする。 An image reading apparatus according to an eighth aspect of the present invention provided to solve the above-mentioned problem is characterized in that, in the first, second, fourth, and fifth aspects, the predetermined value is set in a register.

前記課題を解決するために提供する請求項９の発明に係る画像読取り装置は、請求項３または請求項６の発明において、前記所定値１および／または所定値２は、レジスタ設定されることを特徴とする。 According to a ninth aspect of the present invention, there is provided an image reading apparatus according to a third aspect of the present invention, wherein the predetermined value 1 and / or the predetermined value 2 are set in a register. Features.

本発明の効果として、請求項１，４の発明によれば、差分値の大きさを所定値でスレッシュし、その結果から前ライン黒レベルをプラス、変化なし、マイナスして本ラインの黒レベルを求めることで、ノイズを取るのに最適な値の設定ができる。
請求項２，５の発明によれば、請求項1，４の装置に加え、差分値を累積することで、黒レベルのノイズによる変化を抑えて、黒レベルが丸めのスレッシュにある時でも、黒補正レベルが頻繁に変化を繰り返して画像に悪影響を生じることが無いようにすることができる。
請求項３，６の発明によれば、請求項２，５の装置に加え、差分値が微小な場合に累積値が変化しないため、更に黒レベルのノイズによる変化を抑えて、黒レベルが丸めのスレッシュにある時でも、黒補正レベルが頻繁に変化を繰り返して画像に悪影響を生じることが無いようにすることができる。
また、請求項１〜３の発明は、ラインセンサの特定位置の遮光画素の読取りレベルを遮光レベルとすることにより、請求項４〜６の発明における遮光算出手段を省略したものであり、遮光算出処理を減らしてコストダウンすることができる。なお、請求項４〜６の発明は遮光レベルを平均化して黒レベルとする効果を持っている。
請求項７の発明によれば、電源ON時やADCのリファレンス電圧変更時など遮光画素レベルが大きく変化する時に、請求項１〜６の装置が持つ黒レベルが追従するのに時間を要する欠点を無くすことができるので、黒レベルを即時に追従させることができる。
請求項８，９の発明によれば、ノイズを取るのに最適な値を設定することができる。 As an effect of the present invention, according to the first and fourth aspects of the present invention, the magnitude of the difference value is thresholded by a predetermined value, and the black level of the main line is determined by adding the previous line black level plus, no change, or minus from the result. By obtaining the above, it is possible to set an optimum value for removing noise.
According to the second and fifth aspects of the invention, in addition to the apparatus of the first and fourth aspects, by accumulating the difference values, the change due to the black level noise is suppressed, and even when the black level is in the rounding threshold, It is possible to prevent the black correction level from frequently adversely affecting the image by repeatedly changing.
According to the third and sixth aspects of the invention, in addition to the apparatus of the second and fifth aspects, the accumulated value does not change when the difference value is very small. Even when the threshold value is in the threshold, it is possible to prevent the black correction level from repeatedly changing and causing an adverse effect on the image.
The inventions of claims 1 to 3 omit the shading calculation means in the inventions of claims 4 to 6 by setting the reading level of the shading pixel at a specific position of the line sensor to the shading level. Processing can be reduced and costs can be reduced. The inventions according to claims 4 to 6 have the effect of averaging the light shielding level to the black level.
According to the seventh aspect of the invention, there is a drawback that it takes time for the black level of the device of the first to sixth aspects to follow when the light-shielding pixel level changes greatly, such as when the power is turned on or when the ADC reference voltage is changed. Since it can be eliminated, the black level can be immediately followed.
According to the eighth and ninth aspects of the invention, it is possible to set an optimum value for taking noise.

以下に、本発明に係る画像読取り装置の第１の実施の形態について説明する。
図１に本発明の実施形態に係わる画像読取り装置の構成を示す。
画像読取り装置は、原稿を搭載するコンタクトガラス（１０５)、シェーディングデータ生成用の基準白板(１０１)、ランプ(１０２)および第1ミラーが搭載される第１キャリッジ(１０３)、第２・第３ミラーが搭載される第２キャリッジ(１０４)、１次元ラインセンサの一態様であるＣＣＤイメージセンサ上に縮小結像させるレンズユニット(１０６)、ＣＣＤイメージセンサを搭載したＳＢＵ(１０７)、第１・第２キャリッジを駆動するスキャナモータ(１０８)から構成される。 Hereinafter, a first embodiment of an image reading apparatus according to the present invention will be described.
FIG. 1 shows the configuration of an image reading apparatus according to an embodiment of the present invention.
The image reading apparatus includes a contact glass (105) on which a document is mounted, a reference white plate (101) for generating shading data, a lamp (102), a first carriage (103) on which a first mirror is mounted, second and third. A second carriage (104) on which a mirror is mounted, a lens unit (106) for reducing and forming an image on a CCD image sensor which is an embodiment of a one-dimensional line sensor, an SBU (107) on which a CCD image sensor is mounted, It comprises a scanner motor (108) for driving the second carriage.

上記の構成において、コンタクトガラス(１０５)上に原稿を搭載し、ランプ(１０２)を点灯し、第１・第２キャリッジをスキャナモータ(１０８)により図中右方向に移動走査することにより原稿が読取られる。詳しくは、原稿面にランプ（１０２）からの光が照射され、その反射光が第１〜第３ミラー及びレンズユニット（１０６）を経由してＣＣＤイメージセンサにより読取られる構成において、第１キャリッジ（１０３）及び第２キャリッジがスキャナモータ（１０８）により移動することにより原稿面が１次元ライン状に読取られることが繰り返して行われ、その読取りラインごとにＣＣＤイメージセンサから画像データが出力される構造となっている。 In the above configuration, the original is mounted on the contact glass (105), the lamp (102) is turned on, and the first and second carriages are moved and scanned in the right direction in the figure by the scanner motor (108). Read. Specifically, in the configuration in which light from the lamp (102) is irradiated on the document surface and the reflected light is read by the CCD image sensor via the first to third mirrors and the lens unit (106), the first carriage ( 103) and the second carriage is moved by the scanner motor (108) so that the document surface is repeatedly read in a one-dimensional line, and image data is output from the CCD image sensor for each read line. It has become.

図２は、本発明に係る画像読取り装置における画像データの黒補正処理に関するブロック図である。
図２において、ＣＣＤ（１１）から出力される１次元ライン状の画像データはサンプルホールド、増幅等のアナログ信号処理部（１２）を経て、Ａ／Ｄ変換器（ＡＤＣ）（１３）によりデジタルデータに変換される。 FIG. 2 is a block diagram relating to black correction processing of image data in the image reading apparatus according to the present invention.
In FIG. 2, the one-dimensional line-shaped image data output from the CCD (11) passes through an analog signal processing unit (12) such as sample hold and amplification, and is converted into digital data by an A / D converter (ADC) (13). Is converted to

また、ＣＣＤ（１１）からの１次元ライン状の出力（１ライン出力）は、図３に示すように、読取り有効画素領域外に入力光を遮光した遮光画素領域が設けられている。図２において、黒補正レベル算出部（１４）は、この遮光画素領域の読取りレベルから黒補正レベルを算出し、黒補正部（１５）で、各有効画素の読取りレベルから黒補正レベルの減算を行い、後段の画像処理部に画像データを出力する。後段の画像処理部では、黒補正データが減算された画像データに対して、シェーディング補正、ＭＴＦ補正、ガンマ補正などの画像処理が行われる。 Further, as shown in FIG. 3, a one-dimensional line-like output (one-line output) from the CCD (11) is provided with a light-shielded pixel region that shields input light outside the effective reading pixel region. In FIG. 2, a black correction level calculation unit (14) calculates a black correction level from the reading level of the light-shielded pixel region, and the black correction unit (15) subtracts the black correction level from the reading level of each effective pixel. And output the image data to the subsequent image processing unit. In the subsequent image processing unit, image processing such as shading correction, MTF correction, and gamma correction is performed on the image data obtained by subtracting the black correction data.

なお、ここでは特に詳しく説明しないが、ＣＣＤ（１１）には２ｃｈや４ｃｈ出力のものや、１ｃｈ出力でも内部シフトレジスタが複数ｃｈのものがあり、このような場合、黒補正レベルの算出は各ｃｈ毎に行い、黒補正ではそのｃｈの黒補正レベルを減算するものとする。 Although not specifically described here, the CCD (11) has 2ch and 4ch outputs, and even with 1ch output, the internal shift register has a plurality of channels. In such a case, the black correction level is calculated in each case. This is performed for each channel, and in the black correction, the black correction level of that channel is subtracted.

黒補正レベル算出部（１４）は本発明の根幹をなすものであり、以下に図４を参照しながら、本発明に係わる黒補正レベル算出部を詳細に説明する。
遮光レベル算出手段（２０１）は、ＣＣＤ（１１）が読取った１ラインの複数の遮光画素の読取りレベルから読取りbit数、あるいはそれ以上のbit数で遮光レベルを求める機能を有する。ここで、遮光レベルの算出方法としては、ｎ画素の読取りレベルを平均して求める方法である。画素数ｎは２の乗数個であれば演算が容易であり、また精度を良くするためにbit数は黒レベルのbit数とするのが良い。 The black correction level calculation unit (14) forms the basis of the present invention, and the black correction level calculation unit according to the present invention will be described in detail below with reference to FIG.
The light shielding level calculation means (201) has a function of obtaining the light shielding level from the reading level of a plurality of light shielding pixels of one line read by the CCD (11) by the number of reading bits or more. Here, the light shielding level is calculated by averaging the reading levels of n pixels. If the number of pixels n is a multiplier of 2, the calculation is easy, and the number of bits is preferably the number of bits at the black level in order to improve accuracy.

差分値算出手段（２０２）は、本ラインの遮光レベルと前ラインの黒レベルとの差分値を求める機能を有し、次式により演算を行って差分値を算出する。 The difference value calculation means (202) has a function of obtaining a difference value between the light-shielding level of the main line and the black level of the previous line, and calculates the difference value by performing an operation according to the following equation.

（差分値）＝（遮光レベル）−(前ライン黒レベル) (Difference value) = (shading level)-(front line black level)

黒レベル算出手段（２０４）は、所定値１比較手段（２０５）、黒レベル更新手段（２０６）、黒レベル保存手段（２０７）からなり、差分値と所定値１とを比較し、比較結果から、読取りbit数あるいはそれ以上のbit数で、前ラインの黒レベルを更新して本ラインの黒レベルを求める機能を有する。 The black level calculation means (204) includes a predetermined value 1 comparison means (205), a black level update means (206), and a black level storage means (207), compares the difference value with the predetermined value 1, and determines the comparison result. The function of obtaining the black level of the main line by updating the black level of the previous line with the number of read bits or more.

そのうち、所定値1比較手段（２０５）は、差分値と所定値１とを比較し、差分値がどの領域に属するかにより次に示す３種類の判定信号を出力する。ここで、所定値１はレジスタ設定できるようにしてもよい。 Among them, the predetermined value 1 comparing means (205) compares the difference value with the predetermined value 1, and outputs the following three types of determination signals depending on which region the difference value belongs to. Here, the predetermined value 1 may be set in a register.

（領域１）（差分値）≧（所定値１）の場合、判定信号＝10(b)
（領域２）（所定値１）＞（差分値）＞−（所定値１）の場合、判定信号＝00(b)
（領域３）−（所定値１）≧（差分値）の場合、判定信号＝01(b) When (area 1) (difference value) ≥ (predetermined value 1), judgment signal = 10 (b)
When (area 2) (predetermined value 1)> (difference value)> − (predetermined value 1), determination signal = 00 (b)
If (Region 3)-(Predetermined value 1) ≥ (Difference value), Determination signal = 01 (b)

黒レベル更新手段（２０６）は、上記判定信号によって黒レベル保存手段（２０７）に保存されている（前ライン黒レベル）に基づいて（本ライン黒レベル）を次のように算出する。 The black level update means (206) calculates (main line black level) as follows based on (previous line black level) stored in the black level storage means (207) by the determination signal.

判定信号＝10(b)の場合、(本ライン黒レベル)＝（前ライン黒レベル）＋１ LSB
判定信号＝00(b)の場合、(本ライン黒レベル)＝（前ライン黒レベル）
判定信号＝01(b)の場合、(本ライン黒レベル)＝（前ライン黒レベル）−１ LSB When judgment signal = 10 (b), (main line black level) = (previous line black level) + 1 LSB
When judgment signal = 00 (b), (main line black level) = (previous line black level)
When judgment signal = 01 (b), (main line black level) = (previous line black level)-1 LSB

このように差分値が所定値1より大きいか、所定値1より小さいかにより黒レベルについて加算・減算を行う。なお、更新するビット数（変化ステップ）として、＋１ LSB、−１ LSB としたが、レジスタ設定できるようにしてもよい。 In this way, addition / subtraction is performed on the black level depending on whether the difference value is larger than the predetermined value 1 or smaller than the predetermined value 1. Although the number of bits to be updated (change step) is +1 LSB and -1 LSB, a register may be set.

黒レベル保存手段（２０７）は、黒レベル更新手段（２０６）により算出された（本ライン黒レベル）を保存する。なお、算出した黒レベルに替えて遮光レベルを選択して（本ライン黒レベル）として保存できるようにしてもよい。
また、黒レベルのbit数増加は大きなハード量増加にならないので、高品質に黒補正処理を行うために、読取りbit数よりもbit数を増やす方が良い。 The black level storage unit (207) stores the (main line black level) calculated by the black level update unit (206). Note that, instead of the calculated black level, a shading level may be selected and stored as (main line black level).
In addition, since the increase in the number of bits of the black level does not increase the amount of hardware, it is better to increase the number of bits than the number of read bits in order to perform black correction processing with high quality.

黒補正レベル算出手段（２０３）は、読取りbit数に(本ライン黒レベル)を丸めて黒補正レベルを算出し、保存する。丸めは四捨五入するのが良い。
なお、黒レベルのbit数が読取りbit数の場合は、黒補正レベル算出手段（２０３）は不要となる。 The black correction level calculation means (203) calculates and stores the black correction level by rounding (main line black level) to the number of read bits. Rounding off should be rounded off.
If the number of bits of the black level is the number of read bits, the black correction level calculation means (203) is not necessary.

また、ＣＣＤ１１の特定位置の遮光画素の読取りレベルを遮光レベルとしてもよい。これにより遮光レベル算出手段（２０１）を省略することができる。 Further, the reading level of the light shielding pixel at a specific position of the CCD 11 may be set as the light shielding level. Thereby, the light shielding level calculation means (201) can be omitted.

以上、説明した構成の黒レベル算出部により、所定値１や変化ステップの値でノイズを取るのに最適な設定が可能である。 As described above, the black level calculation unit having the above-described configuration can be set optimally for taking noise at the predetermined value 1 or the change step value.

つぎに、本発明に係る画像読取り装置の第２の実施の形態について説明する。
本発明も黒レベル算出部に特徴があり、その構成を図５に示す。第１の実施の形態における黒レベル算出部に新たな機能を有する手段が追加された構成であり、以下に第１の実施の形態（図４）との違いだけを説明する。 Next, a second embodiment of the image reading apparatus according to the present invention will be described.
The present invention is also characterized by a black level calculation unit, and its configuration is shown in FIG. A means having a new function is added to the black level calculation unit in the first embodiment, and only differences from the first embodiment (FIG. 4) will be described below.

累積値算出・保存手段（２０８）は、差分値を累積していく。即ち、保存されている（前ライン累積値）に差分値を加え(差分値がマイナスの場合は減算となる)、（本ライン累積値）として保存する機能を有する。
また、黒レベル更新手段（２０６）からクリア信号パルスが入力された場合、保存している（本ライン累積値）をクリアする。 The accumulated value calculating / storing means (208) accumulates the difference values. That is, it has a function of adding a difference value to the stored (previous line accumulated value) (subtracting when the difference value is negative) and saving it as (main line accumulated value).
Further, when a clear signal pulse is input from the black level update means (206), the stored (the accumulated value of this line) is cleared.

所定値１比較手段（２０５）以降は、第１の実施の形態における差分値が累積値となるのみで、同じ処理が施される。なお、黒レベル更新手段（２０６）において、判定信号＝10(b)または01(b)であり、（本ライン黒レベル）が（前ライン黒レベル）から変化する場合には、前記累積値算出・保存手段（２０８）にクリア信号パルスを出力する動作が加わる。 After the predetermined value 1 comparing means (205), only the difference value in the first embodiment becomes an accumulated value, and the same processing is performed. In the black level update means (206), when the determination signal = 10 (b) or 01 (b) and (main line black level) changes from (previous line black level), the cumulative value calculation is performed. An operation for outputting a clear signal pulse is added to the storage means (208).

以上、説明した構成の黒レベル算出部により、差分値を累積することで、黒レベルのノイズによる変化を抑えて、黒レベルが丸めのスレッシュにある時でも、黒補正レベルが頻繁に変化を繰り返して画像に悪影響を及ぼすことをなくすことができる。 As described above, the black level calculation unit configured as described above accumulates the difference value to suppress the change due to the noise of the black level, and the black correction level frequently repeats even when the black level is at the rounding threshold. This can eliminate adverse effects on the image.

つぎに、本発明に係る画像読取り装置の第３の実施の形態について説明する。
本発明も黒レベル算出部に特徴があり、その構成を図６に示す。第２の実施の形態における黒レベル算出部に新たな機能を有する手段が追加された構成であり、以下に第２の実施の形態（図５）との違いだけを説明する。 Next, a third embodiment of the image reading apparatus according to the present invention will be described.
The present invention is also characterized by a black level calculation unit, and its configuration is shown in FIG. In the second embodiment, means having a new function is added to the black level calculation unit in the second embodiment, and only differences from the second embodiment (FIG. 5) will be described below.

所定値２比較手段（２０９）は、差分値と所定値２とを比較し、差分値がどの領域に属するかにより次に示す３種類の判定信号を出力する。 The predetermined value 2 comparing means (209) compares the difference value with the predetermined value 2, and outputs the following three types of determination signals depending on which region the difference value belongs to.

（領域１）（差分値）≧（所定値２）の場合、判定信号＝10(b)
（領域２）（所定値２）＞（差分値）＞−（所定値２）の場合、判定信号＝00(b)
（領域３）−（所定値２）≧（差分値）の場合、判定信号＝01(b) When (area 1) (difference value) ≥ (predetermined value 2), judgment signal = 10 (b)
When (area 2) (predetermined value 2)> (difference value)> − (predetermined value 2), determination signal = 00 (b)
If (Region 3)-(Predetermined value 2) ≥ (Difference value), Determination signal = 01 (b)

累積値算出・保存手段（２０８）は、上記判定信号によって保存されている（前ライン累積値）から（本ライン累積値）を次のように算出し、算出した（本ライン累積値）を保存する。 Cumulative value calculation / storage means (208) calculates (main line cumulative value) from (previous line cumulative value) stored by the determination signal as follows, and stores the calculated (main line cumulative value). To do.

判定信号＝10(b)の場合、(本ライン累積値)＝（前ライン累積値）＋１ LSB
判定信号＝00(b)の場合、(本ライン累積値)＝（前ライン累積値）
判定信号＝01(b)の場合、(本ライン累積値)＝（前ライン累積値）−１ LSB When judgment signal = 10 (b), (main line accumulated value) = (previous line accumulated value) + 1 LSB
When judgment signal = 00 (b), (main line accumulated value) = (previous line accumulated value)
When judgment signal = 01 (b), (main line accumulated value) = (previous line accumulated value)-1 LSB

以上、説明した構成の黒レベル算出部により、差分値が微小な場合には累積値が変化しないため、更に黒レベルのノイズによる変化を抑えて、黒レベルが丸めのスレッシュにある時でも、黒補正レベルが頻繁に変化を繰り返して画像に悪影響を及ぼすことをなくすことができる。 As described above, the accumulated value does not change when the difference value is small by the black level calculation unit having the above-described configuration. Therefore, even when the black level is at the rounding threshold by suppressing the change due to the noise of the black level. It is possible to prevent the correction level from changing frequently and adversely affecting the image.

本発明に係る画像読取り装置の構成図である。1 is a configuration diagram of an image reading apparatus according to the present invention. 本発明に係る画像読取り装置における画像データの黒補正処理に関するブロック図である。FIG. 6 is a block diagram relating to black correction processing of image data in the image reading apparatus according to the present invention. １次元ラインセンサ（ＣＣＤ）の１ライン出力状態を示す図である。It is a figure which shows the 1 line output state of a one-dimensional line sensor (CCD). 本発明に係る画像読取り装置の第１の実施の形態における黒補正レベル算出部の構成図である。It is a block diagram of the black correction level calculation part in 1st Embodiment of the image reader which concerns on this invention. 本発明に係る画像読取り装置の第２の実施の形態における黒補正レベル算出部の構成図である。It is a block diagram of the black correction level calculation part in 2nd Embodiment of the image reader which concerns on this invention. 本発明に係る画像読取り装置の第３の実施の形態における黒補正レベル算出部の構成図である。It is a block diagram of the black correction level calculation part in 3rd Embodiment of the image reader which concerns on this invention.

Explanation of symbols

１１ＣＣＤ
１２アナログ信号処理
１３Ａ／Ｄ変換器（ＡＤＣ）
１４黒補正レベル算出部
１５黒補正部
１０１基準白板
１０２スキャナランプ
１０３第１キャリッジ
１０４第２キャリッジ
１０５コンタクトガラス
１０６レンズ
１０７ＳＢＵ
１０８スキャナモータ
１０９スキャナＨ．Ｐ．センサ
２０１遮光レベル算出手段
２０２差分値算出手段
２０３黒補正レベル算出手段
２０４黒レベル算出手段
２０５所定値１比較手段
２０６黒レベル更新手段
２０７黒レベル保存手段
２０８累積値算出・保存手段
２０９所定値２比較手段

11 CCD
12 Analog signal processing 13 A / D converter (ADC)
14 Black correction level calculation unit 15 Black correction unit 101 Reference white plate 102 Scanner lamp 103 First carriage 104 Second carriage 105 Contact glass 106 Lens 107 SBU
108 Scanner motor 109 Scanner H. P. Sensor 201 Shading level calculation means 202 Difference value calculation means 203 Black correction level calculation means 204 Black level calculation means 205 Predetermined value 1 comparison means 206 Black level update means 207 Black level storage means 208 Accumulated value calculation / storage means 209 Predetermined value 2 comparison means

Claims

Scanning a document surface optically and reading it in a one-dimensional line is repeated, and a line sensor that outputs image data for each line and reading of light-shielded pixels provided outside the effective pixel area of the line sensor. A black correction level calculation unit that obtains a black correction level from the level, and a black correction unit that obtains a true reading level by subtracting the black correction level from the reading level of the effective pixel of the image data for each reading line. In an image reader,
The black correction level calculation unit
A difference value calculating means for obtaining a difference value between a light shielding level which is a reading level of a light shielding pixel at a specific position of the line sensor and a black level of the previous line;
A black level calculation means for comparing the difference value with a predetermined value, and updating the black level of the previous line with the number of read bits or more from the comparison result to obtain the black level of the main line;
A black correction level calculating means for obtaining a black correction level of the main line of the number of read bits from the black level of the main line and outputting the black correction level to the black correction unit;
An image reading apparatus comprising:

Scanning a document surface optically and reading it in a one-dimensional line is repeated, and a line sensor that outputs image data for each line and reading of light-shielded pixels provided outside the effective pixel area of the line sensor. A black correction level calculation unit that obtains a black correction level from the level, and a black correction unit that obtains a true reading level by subtracting the black correction level from the reading level of the effective pixel of the image data for each reading line. In an image reader,
The black correction level calculation unit
A difference value calculating means for obtaining a difference value between a light shielding level which is a reading level of a light shielding pixel at a specific position of the line sensor and a black level of the previous line;
A cumulative value calculating means for adding the differential value to the cumulative value of the differential value up to the previous line and obtaining a new cumulative value;
A black level calculating means for comparing the obtained cumulative value with a predetermined value, and updating the black level of the previous line with the number of read bits or more from the comparison result to obtain the black level of the main line;
A black correction level calculating means for obtaining a black correction level of the main line of the number of read bits from the black level of the main line and outputting the black correction level to the black correction unit;
An image reading apparatus comprising:

Scanning a document surface optically and reading it in a one-dimensional line is repeated, and a line sensor that outputs image data for each line and reading of light-shielded pixels provided outside the effective pixel area of the line sensor. A black correction level calculation unit that obtains a black correction level from the level, and a black correction unit that obtains a true reading level by subtracting the black correction level from the reading level of the effective pixel of the image data for each reading line. In an image reader,
The black correction level calculation unit
A difference value calculating means for obtaining a difference value between a light shielding level which is a reading level of a light shielding pixel at a specific position of the line sensor and a black level of the previous line;
Means for comparing the difference value with the predetermined value 2 and updating a cumulative value from the comparison result up to the previous line to obtain a new cumulative value;
Black level calculation means for comparing the obtained accumulated value with a predetermined value 1 and updating the black level of the previous line with the number of read bits or more from the comparison result to obtain the black level of this line; ,
A black correction level calculating means for obtaining a black correction level of the main line of the number of read bits from the black level of the main line and outputting the black correction level to the black correction unit;
An image reading apparatus comprising:

Scanning a document surface optically and reading it in a one-dimensional line is repeated, and a line sensor that outputs image data for each line and reading of light-shielded pixels provided outside the effective pixel area of the line sensor. A black correction level calculation unit that obtains a black correction level from the level, and a black correction unit that obtains a true reading level by subtracting the black correction level from the reading level of the effective pixel of the image data for each reading line. In an image reader,
The black correction level calculation unit
A light-shielding level calculating means for obtaining a light-shielding level with the number of read bits or the number of bits higher than the number of read bits from the read level of a plurality of light-shielded pixels in one line read by the line sensor;
Difference value calculating means for obtaining a difference value between the light shielding level and the black level of the previous line;
A black level calculation means for comparing the difference value with a predetermined value, and updating the black level of the previous line with the number of read bits or more from the comparison result to obtain the black level of the main line;
A black correction level calculating means for obtaining a black correction level of the main line of the number of read bits from the black level of the main line and outputting the black correction level to the black correction unit;
An image reading apparatus comprising:

Scanning a document surface optically and reading it in a one-dimensional line is repeated, and a line sensor that outputs image data for each line and reading of light-shielded pixels provided outside the effective pixel area of the line sensor. A black correction level calculation unit that obtains a black correction level from the level, and a black correction unit that obtains a true reading level by subtracting the black correction level from the reading level of the effective pixel of the image data for each reading line. In an image reader,
The black correction level calculation unit
A light-shielding level calculating means for obtaining a light-shielding level from the reading level of a plurality of light-shielding pixels of the line sensor, or the number of read bits, or more than,
Difference value calculating means for obtaining a difference value between the light shielding level and the black level of the previous line;
A cumulative value calculating means for adding the differential value to the cumulative value of the differential value up to the previous line and obtaining a new cumulative value;
A black level calculating means for comparing the obtained cumulative value with a predetermined value, and updating the black level of the previous line with the number of read bits or more from the comparison result to obtain the black level of the main line;
A black correction level calculation means for obtaining the black correction level of the main line of the number of read bits from the black level of the main line and outputting the black correction level to the black correction unit;
An image reading apparatus comprising:

Scanning a document surface optically and reading it in a one-dimensional line is repeated, and a line sensor that outputs image data for each line and reading of light-shielded pixels provided outside the effective pixel area of the line sensor. A black correction level calculation unit that obtains a black correction level from the level, and a black correction unit that obtains a true reading level by subtracting the black correction level from the reading level of the effective pixel of the image data for each reading line. In an image reader,
The black correction level calculation unit
A light-shielding level calculating means for obtaining a light-shielding level from the reading level of a plurality of light-shielding pixels of the line sensor, or the number of read bits, or more than,
Difference value calculating means for obtaining a difference value between the light shielding level and the black level of the previous line;
Means for comparing the difference value with the predetermined value 2 and updating a cumulative value from the comparison result up to the previous line to obtain a new cumulative value;
Black level calculation means for comparing the obtained accumulated value with a predetermined value 1 and updating the black level of the previous line with the number of read bits or more from the comparison result to obtain the black level of this line; ,
A black correction level calculation means for obtaining the black correction level of the main line of the number of read bits from the black level of the main line and outputting the black correction level to the black correction unit;
An image reading apparatus comprising:

7. The black level calculating means has a function of setting the shading level to a black level of the main line, and the function is selected by a hardware signal for register setting or reading operation control. The image reading apparatus according to any one of the above.

6. The image reading apparatus according to claim 1, wherein the predetermined value is set in a register.

7. The image reading apparatus according to claim 3, wherein the predetermined value 1 and / or the predetermined value 2 are set in a register.